It turns out, being "allergic to exercise" isn't just an excuse to pour another glass of wine and skip the gym. For some, this is a real condition called exercise-induced anaphylaxis—and it's not as fun as it sounds. In fact, it's pretty serious.

For those with the allergy, exercise can result in flushing of the skin, hives, swelling, and nausea, among other symptoms. But before you worry about going on a jog or hitting the elliptical, know the chances of having an allergic reaction to physical activity are rare. Exercise-induced anaphylaxis, first described in 1979, is uncommon and probably affects around 50 in every 100,000 people, reports Popular Science. However, if you do experience any severe reactions to exercise, here's what you should know:

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The "why" is still unclear.

Maria Castells, an allergist at Brigham and Women's Hospital, told the publication that although awareness of the condition has increased, researchers and doctors still don't know exactly why it occurs.

There are some theories, but it's hard to re-create the condition for testing in a lab. "There's no mouse model and no human model of the ideas," Castells said. "There are a number of groups trying to develop a model, but they need more time."

A variety of factors can cause an allergic reaction to exercise.

The most common cause of a reaction is food plus exercise, known as food-dependent, exercise-induced anaphylaxis, which affects between 30 to 50 percent of people with the allergy. According to an Anaphylaxis Campaign fact-sheet, symptoms occur when a particular "trigger" food is eaten before exercise. Wheat and shellfish are common culprits.

For others, aspirin plus exercise is to blame. Symptoms can occur when aspirin is taken on the same day the exercise occurs. And if someone with the allergy ate a trigger food, took aspirin, and exercised, more severe symptoms could develop, such as a swollen tongue, difficulty swallowing, or feeling faint or weak.

Some women only experience symptoms during their menstrual cycle because high levels of estrogen can bind to the cells involved with an allergic reaction. "And for a proportion it's nothing, really, just the exercise itself," Castells added.

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The amount of exercise needed to trigger a reaction depends on the person.

Here's one more reason to stay in shape: In general, people who are physically fit are less susceptible to an allergic reaction from exercise than people who aren't, Castells said. Those with the condition might want to think about taking up swimming: almost all other types of exercise, like running, dancing, or biking, have been reported to cause an allergic reaction, Castells explained, but not swimming.

Exercise-induced anaphylaxis is manageable.

According to Anaphylaxis Campaign, medical experts recommend avoiding physical activity on the day they eat their trigger food or drug. However, if possible, it's safest to avoid the triggers altogether so you can ensure exercise without any negative reactions.

In addition to preventative treatment, symptoms can also be treated with EpiPens containing adrenaline. These are prescribed for people believed to be at risk, and you should have them readily available at all times to be used as soon as a severe reaction starts to occur.

If you've yet to experience any symptoms, there is no reason to toss out your running shoes and gym bag. Physical activity is good for us, whether we enjoy it or not, but if you do have a reaction during exercise, contact a health professional to determine the cause and find a plan that works best for you.